Properties of two spliceoforms of major ampullate spidroin 1 reveal unique functions of N-linker region

Abstract

Spiders produce diverse silk fibers with distinct properties for daily survival. Among these silk fibers, dragline silk spun by major ampullate gland is used for bridgelines and web radii, exhibiting both outstanding tensile strength and extensibility. Although more and more full-length major ampullate spidroin gene sequences have been reported, the research regarding alternative splicing events of spidroins are rare. Here we describe two spliceoforms of major ampullate spidroin 1 (MaSp1) from Araneus ventricosus, and both of them are lack of central repetitive region. The minor isoform only has terminal regions. For the major isoform, however, the N-linker and terminal regions are all retained. Furthermore, we investigated the functions of N-linker structure of A. ventricosus MaSp1, based on the properties of the two spliceoforms. The dimer level of major isoform (MaSp1-2) is higher than that of the minor isoform (MaSp1-1). Moreover, the MaSp1-2 protein display higher melting temperature (Tm) than MaSp1-1, and the MaSp1-2 fibers exhibit higher tensile strength than MaSp1-1 fibers. These studies demonstrate that the N-linker region promotes the formation of intermolecular disulphide bond, suggesting a strategy to enhance the thermostabilization and mechanical properties of spidroins.